The present invention relates to treatment of waste pneumatic tires and similar tough, resilient materials, and particularly relates to a method and apparatus for reducing scrap tires into pieces which are small enough to be handled and transported easily and to be useful for further processing.
Huge numbers of unusable pneumatic tire carcasses are discarded annually. These tire carcasses contain quantities of synthetic and natural rubber material which is useful for many different purposes, except for the fact that the bulkiness of tires has made it uneconomical in the past to recover the materials of which they are made. Many different machines have been made which are able to reduce whole tires into smaller pieces of various sizes, at various rates, and with different amounts of reliability. Some of these machines are able to cut whole tires into smaller pieces at a high rate, but the pieces produced may still be too large for many applications. Examples of such machines are those of the type disclosed in Holman, U.S. Pat. No. 3,931,935, Rouse et al., U.S. Pat. No. 4,374,573, and Rouse et al., U.S. Pat. No. 4,560,112. These machines are capable of reducing whole automobile and truck tires into smaller pieces, most of which are elongate strips, with a single pass through the machine.
Kisielewski, U.S. Pat. No. 4,156,508 suggests passing the larger ones of those pieces a second time through the same shredder in order to reduce the pieces to a smaller size. This method, however, reduces the number of tires which can be shredded by the machines in a given amount of time.
Plastics granulator machines which have been known previously are also useful in reducing pieces of rubber to smaller sizes. One such machine which has proven useful for pieces of rubber tires is the Model 3250 granulator manufactured by Cumberland Engineering, a Division of Leesona Corporation, of Attleboro, Mass. It includes stationary horizontal knives, and several short blades attached to a hub which rotates rapidly about a horizontal axis to reduce pieces of material including tough resilient material such as tire rubber into smaller pieces by shearing or crushing the material between the short blades and the horizontal knives. A screen surrounding the rotating knives retains pieces of material which have been fed into the apparatus, until they have been reduced to an acceptably small size and are able to escape by passing through the screen. Apparatus of this type is unable to handle large pieces of rubber such as whole tires efficiently, but has been used in the past to reduce to an acceptable size the pieces which have been produced by cutting apart whole tires. Such granulators operate with rubber most efficiently if fed smaller pieces of rubber at a steady rate and if the reduction in size required in the granulator is not too great.
Pneumatic tire casings often contain metal wires, both as tread reinforcements and in the bead portions of the tires. Such reinforcing materials interfere with some uses of the pieces of rubber which can be produced by cutting tires, but are themselves of value when reclaimed.
Feeding whole tires into shredding apparatus is frequently subject to short interruptions and often produces an output of shredded tires which is not completely steady. Occasionally, such apparatus becomes temporarily overloaded and must be stopped and cleared before disposal of such whole tires can be continued. Preferably, this should not interfere with the rate of production of small pieces of material.
None of the previously-known apparatus or methods, however, have provided adequately for reducing entire automobile and truck tires and similar tough, resilient objects and materials into small pieces, having maximum dimensions on the order of one inch or less, which are easily transported and useful for chemical treatment or further mechanical treatment and subsequent reuse of the materials or components thereof.
What is needed, then, is apparatus and a method for its use for reducing relatively large pieces of tough resilient materials, such as vehicle tires, into small pieces at a high rate and a steady output which is not dependent on providing a completely continuous flow of whole tires into the apparatus.